1. Field of the Invention
The present invention relates in general to a two-axis ball-based cursor control apparatus, such as a mouse or trackball, and in particular to a cursor control apparatus which provides the user with tactile feedback corresponding to uniform incremental movements of a displayed cursor.
2. Background Art
Two-axis cursor control devices are well-known in the art. These types of devices are common components of personal computer systems used for controlling the movement of a cursor appearing on a video monitor. Cursor control devices are also finding use in handheld devices such as PDA's and cellular telephones where graphical user interfaces are manipulated by the user. Two well-known forms of such devices include the computer mouse and the trackball. A computer mouse typically consists of a spherical ball, approximately one-half inch in diameter and freely rotatable about two axes of rotation, mounted within a larger housing which rests on a flat surface, so that a portion of the ball protrudes from the bottom of the housing and comes into contact with the surface. Typically, a pair of rotors are positioned in contact with the ball, one aligned with each axis. Each of these rotors are in turn connected to a disk-shaped apparatus with uniformly spaced holes around the outer portion of the disk. When the mouse is moved along the flat surface, the rotation of the ball is translated to the rotors, and in turn to the associated disks. Light sensors positioned near each of the disks determine the number of times a beam of light passing through a hole in the disk is interrupted as the disk rotates. From this signal, the direction and acceleration of the displacement of the ball, and hence of the mouse itself, is determined. This information is then translated into motion of the cursor on the screen of the computer using a predetermined relationship between the magnitude of the mouse displacement in each direction and the distance which the cursor moves in that direction. Thus, the user's horizontal and vertical movement of the mouse on the flat surface is translated into horizontal and vertical movement of the cursor on the screen.
A trackball is a similar type of cursor control apparatus in which the user merely rotates the ball itself instead of moving the entire housing. The ball typically protrudes from the top of its housing, where it can be rotated directly by the user by hand. The remainder of the device is typically substantially similar to that described above, with the rotation of the ball translated to a pair of rotors associated with each axis of rotation, and then to a pair of disks, whose motion is then translated into cursor motion by light sensors. Thus, unlike a mouse, a trackball apparatus remains stationary while the user directly rotates the ball itself.
There are, however, certain disadvantages to these types of cursor control devices. In order to achieve precise targeting of the cursor, the user must possess a certain degree of hand to eye coordination to align the cursor with the desired location. This can be troublesome in certain applications, such as pull-down menus implemented in PC graphical user interface based operating systems. Typically a single mouse click causes a number of further commands or options to appear in row after row. To select a give command or option the user must position the cursor over the text label for the desired option to execute same. Any slight movement of the device by the user will cause the cursor displayed on the screen to move to a different command or option item than that desired. Positioning is accomplished by moving the mouse or trackball, which moves in one continuous motion, until the cursor is in position. The absence of any tactile feedback corresponding to the movement of the cursor makes such precise targeting even more difficult. In addition, some devices have a tendency for the cursor to drift from its desired location because any slight or unintentional force exerted on the control device will cause it to move, and correspondingly displace the cursor from the desired location. In applications where precise targeting and control of the cursor is essential, for instance in computer aided drafting, these drawbacks are particularly unwelcome. Incorporating graphical user interfaces into smaller devices, such as cellular phones, causes potential safety issues. For example, a person using a phone in a car to recall a speed dial number using the graphical interface may cause an accident by trying to align a cursor over the display of names or numbers stored in memory.
Also known in the prior art are control devices consisting of a rotatable disk or wheel which is rotatable about only one axis in discrete, uniform increments. Examples of such devices include dials for applications such as frame-by-frame movement in a video-disc player or to switch tracks on an audio-disc player. Such devices may provide tactile feedback to the user in the form of a “clicking” or ratcheting effect which occurs when the disk or wheel is rotated. The user knows when such a device has advanced from one position to the next because of the tactile sensation triggered by the dial “snapping” into the next position. Such known devices, however, have the disadvantage of providing such incremental rotation about only one axis, therefore making them ill-suited for applications requiring control of a cursor moving in two dimensions.
It would therefore be desirable to provide a cursor control device which would allow the user to move the cursor in discrete, uniform increments in two dimensions, in order to more easily achieve precise targeting of the cursor with its intended position on the screen. Further, it would also be desirable to provide for such a device which provides tactile feedback to the user which corresponds to the movement of the cursor on the screen. In addition, it would be desirable to provide for such a device in which the unintentional motion of the cursor due to inadvertent movement of the device is minimized.
These and other objects of the present invention will become apparent to those of ordinary skill in the art in light of the present specifications, drawings, and claims.